Hybrid vehicles, such as hybrid electric vehicles (HEV) or plugin-in hybrid electric vehicles (PHEV), typically comprise a drive train with a gearbox for allowing the vehicle to use different gears at different speeds. This practice is common both for hybrid vehicles and traditional vehicles, such as vehicles with single internal combustion engines.
Transmission arrangements for hybrid vehicles in difference from transmission arrangements for traditional vehicles need to be adapted for power input from multiple sources. In addition, hybrid vehicles are often produced to be energy efficient and thereby needs to utilize energy efficient gearboxes.
In prior art it is well known to use dual-clutch transmissions for vehicles in order to decrease the time of gear changes and optimize fuel consumption in relation to use of traditional automatic gearboxes or manual gearboxes. The dual-clutch transmission can fundamentally be described as two manual gearboxes working as one unit while contained within a single housing. In general, dual-clutch gearboxes comprise a twin-clutch configuration creating a semi-automatic or fully automatic gearbox that can prepare the next gear prior to a gear change by utilizing the two clutches in combination with two input shafts. Thereby the time required to switch into the next gear is minimized and fuel is saved. One further advantage with the dual-clutch transmission arrangement is that the hydraulic clutch associated with traditional automatic gearboxes can be removed. This is beneficial in relation to fuel saving.
The implementation of extra parts, such as the dual-clutch configuration, presents problems in relation to the size of the gearbox. This is a difficult problem especially for gearboxes with a high number of gears wherein it is desired to minimize the number of dependencies between the gears. A gear dependency is when at least two driven gears are driven by the same drive gear. E.g., a fourth and a sixth drive gear of a transmission both mesh with and are driven by one drive gear upon an input shaft. A change in gear ratio of the fourth drive gear would thereby affect the gear ratio of the sixth drive gear and vice versa. Furthermore, transversal installation of internal combustion engines provides an even greater challenge regarding fitting all the necessary components within the confined space of an engine bay. Modern vehicles require strict safety standards which limit the space within engine bays even more due to structural reinforcements and deformation zones.
Hybrid vehicles are characterized by their multiple engines and/or drive sources that are used to power the vehicle. The addition of an extra engine presents even more difficulties in relation to the available space and the difficulties encountered when fitting all the components in a vehicle. For hybrid electric vehicles wherein an internal combustion engine is combined with an electrical engine two different propulsion systems need to be connected to the transmission. This means that the drive train and gearbox needs to be adapted to the requirements of different propulsion systems. This adds additional modifications to the drive train of such vehicles which increase the size of the transmission. It is thereby essential for hybrid vehicles to comprise compact transmissions in order to maintain the size of such vehicles.
The conventional design of dual-clutch transmission arrangements for use with transverse internal combustion engine arrangements comprises gearboxes with six or less gears excluding the reverse gear. Furthermore, the conventional designs depend on multiple dependencies between gears as well as gear configurations that might mix even and odd gears in ways that limits the gear ratio of the gearbox. It is for example common to arrange both the lowest and highest gears at the same output shaft in compact dual-clutch gearboxes which limits the gear ratio options available. For example, by comprising the entire range of gears in a gearbox at one single output shaft, that single output shaft has to be adapted to conform to both the highest and lowest gear ratio that is possible for the gearbox to deliver. This limits the available options and especially decreases the options of reducing the gearbox size due to the limitations in drive gear options.
Creation of compact gearboxes thereby presents additional problems to address in relation of how to distribute the gears within the gearbox without increasing the size of the gearbox housing. It is beneficial to achieve as high gear ratio ranges as possible by creating a gearbox where the gear ratio between the lowest and highest gear can be decided without limiting factors such as gear dependencies.
With the above problems and solutions in mind it would therefore be advantageous to provide a compact dual-clutch transmission arrangement for a transverse engine arrangement in a hybrid vehicle that decreases, or maintains, the size of the gearbox housing while providing sufficient options in relation to gear dependencies and gear ratio.